The present invention relates to a focus detecting device for a camera. More particularly, the invention relates to a focus detecting device employing an infrared beam for focus detection which passes through the photographing lens of the camera.
A variety of devices in which an infrared beam is utilized for focus detection have been proposed in the art. In the case where the device is used with a single-lens reflex camera having an interchangeable lens, that is, where it is utilized as a TTL (Through The Lens) focus detecting device, in an ordinary photographing lens in which the focused position changes with the wavelength of the light (i.e., where chromatic aberration is corrected only in the visible region), the visible beam focused position does not coincide with the infrared beam focused position. In addition, different photographing lenses exhibit a difference between the visible beam focused position and the infrared beam focused position. Therefore, the photographing lenses must be individually corrected.